É possibile creare plugin nel linguaggio di programmazione Python. A differenza dei classici plugin scritti in C++ questi dovrebbero essere piú facili da scrivere, capire, mantenere e distribuire grazie alla natura dinamica del linguaggio Python.
Python plugins are listed together with C++ plugins in QGIS plugin manager.
They are searched for in these paths:
Scrivere un plugin
Since the introduction of Python plugins in QGIS, a number of plugins have
appeared - on Plugin Repositories wiki page
you can find some of them, you can use their source to learn more about
programming with PyQGIS or find out whether you are not duplicating development
effort. The QGIS team also maintains an Official python plugin repository.
Ready to create a plugin but no idea what to do? Python Plugin Ideas wiki
page lists wishes from the
community!
File del plugin
Here’s the directory structure of our example plugin
PYTHON_PLUGINS_PATH/
MyPlugin/
__init__.py --> *required*
mainPlugin.py --> *required*
metadata.txt --> *required*
resources.qrc --> *likely useful*
resources.py --> *compiled version, likely useful*
form.ui --> *likely useful*
form.py --> *compiled version, likely useful*
Qual é il significato dei files:
Here
is an online automated way of creating the basic files (skeleton) of a typical
QGIS Python plugin.
Also there is a QGIS plugin called Plugin Builder
that creates plugin template from QGIS and doesn’t require internet connection.
This is the recommended option, as it produces 2.0 compatible sources.
Contenuto del plugin
Qui puoi trovare informazioni ed esempi su cosa aggiungere in ognuno dei file nella struttura descritta sopra.
__init__.py
This file is required by Python’s import system. Also, QGIS requires that this
file contains a classFactory() function, which is called when the
plugin gets loaded to QGIS. It receives reference to instance of
QgisInterface and must return instance of your plugin’s class from the
mainplugin.py — in our case it’s called TestPlugin (see below).
This is how __init__.py should look like
def classFactory(iface):
from mainPlugin import TestPlugin
return TestPlugin(iface)
## any other initialisation needed
mainPlugin.py
This is where the magic happens and this is how magic looks like:
(e.g. mainPlugin.py)
from PyQt4.QtCore import *
from PyQt4.QtGui import *
from qgis.core import *
# initialize Qt resources from file resources.py
import resources
class TestPlugin:
def __init__(self, iface):
# save reference to the QGIS interface
self.iface = iface
def initGui(self):
# create action that will start plugin configuration
self.action = QAction(QIcon(":/plugins/testplug/icon.png"), "Test plugin", self.iface.mainWindow())
self.action.setObjectName("testAction")
self.action.setWhatsThis("Configuration for test plugin")
self.action.setStatusTip("This is status tip")
QObject.connect(self.action, SIGNAL("triggered()"), self.run)
# add toolbar button and menu item
self.iface.addToolBarIcon(self.action)
self.iface.addPluginToMenu("&Test plugins", self.action)
# connect to signal renderComplete which is emitted when canvas
# rendering is done
QObject.connect(self.iface.mapCanvas(), SIGNAL("renderComplete(QPainter *)"), self.renderTest)
def unload(self):
# remove the plugin menu item and icon
self.iface.removePluginMenu("&Test plugins", self.action)
self.iface.removeToolBarIcon(self.action)
# disconnect form signal of the canvas
QObject.disconnect(self.iface.mapCanvas(), SIGNAL("renderComplete(QPainter *)"), self.renderTest)
def run(self):
# create and show a configuration dialog or something similar
print "TestPlugin: run called!"
def renderTest(self, painter):
# use painter for drawing to map canvas
print "TestPlugin: renderTest called!"
The only plugin functions that must exist in the main plugin source file (e.g.
mainPlugin.py) are:
- __init__ –> which gives access to QGIS interface
- initGui() –> called when the plugin is loaded
- unload() –> called when the plugin is unloaded
You can see that in the above example, the addPluginToMenu() is used.
This will add the corresponding menu action to the
menu. Alternative methods exist to add the action to a different menu. Here is
a list of those methods:
- addPluginToRasterMenu()
- addPluginToVectorMenu()
- addPluginToDatabaseMenu()
- addPluginToWebMenu()
Hanno tutti la stessa sintassi del metodo addPluginToMenu().
Aggiungere il menu del tuo plugin ad uno di questi metodi predefiniti é raccomandato per mantenere la consistenza riguardo all’organizzazione dei plugin. É comunque possibile aggiungere un gruppo personalizzato alla barra dei menu, come dimostrato nel prossimo esempio:
def initGui(self):
self.menu = QMenu(self.iface.mainWindow())
self.menu.setObjectName("testMenu")
self.menu.setTitle("MyMenu")
self.action = QAction(QIcon(":/plugins/testplug/icon.png"), "Test plugin", self.iface.mainWindow())
self.action.setObjectName("testAction")
self.action.setWhatsThis("Configuration for test plugin")
self.action.setStatusTip("This is status tip")
QObject.connect(self.action, SIGNAL("triggered()"), self.run)
self.menu.addAction(self.action)
menuBar = self.iface.mainWindow().menuBar()
menuBar.insertMenu(self.iface.firstRightStandardMenu().menuAction(), self.menu)
def unload(self):
self.menu.deleteLater()
Don’t forget to set QAction and QMenu objectName to a name
specific to your plugin so that it can be customized.
Resource File
You can see that in initGui() we’ve used an icon from the resource file
(called resources.qrc in our case)
<RCC>
<qresource prefix="/plugins/testplug" >
<file>icon.png</file>
</qresource>
</RCC>
It is good to use a prefix that will not collide with other plugins or any
parts of QGIS, otherwise you might get resources you did not want. Now you
just need to generate a Python file that will contain the resources. It’s
done with pyrcc4 command
pyrcc4 -o resources.py resources.qrc
And that’s all... nothing complicated :)
If you’ve done everything correctly you should be able to find and load
your plugin in the plugin manager and see a message in console when toolbar
icon or appropriate menu item is selected.
When working on a real plugin it’s wise to write the plugin in another
(working) directory and create a makefile which will generate UI + resource
files and install the plugin to your QGIS installation.
Documentazione
The documentation for the plugin can be written as HTML help files. The
qgis.utils module provides a function, showPluginHelp() which
will open the help file browser, in the same way as other QGIS help.
The showPluginHelp`() function looks for help files in the same
directory as the calling module. It will look for, in turn,
index-ll_cc.html, index-ll.html, index-en.html,
index-en_us.html and index.html, displaying whichever it finds
first. Here ll_cc is the QGIS locale. This allows multiple translations of
the documentation to be included with the plugin.
The showPluginHelp() function can also take parameters packageName,
which identifies a specific plugin for which the help will be displayed,
filename, which can replace “index” in the names of files being searched,
and section, which is the name of an html anchor tag in the document
on which the browser will be positioned.